Optical cavities are used for controlling, confining or otherwise passing light for a variety of arrangements and applications. These applications include lasers, quantum information networks, optical memory devices, integrated optical circuits for optical communications and interconnects, emitters, and resonators. Optical cavities, and in particular optical microcavities, have a relatively thin layer in which light is confined, sometimes referred to as a spacer layer, with reflective material on faces of the thin layer to confine the light. These microcavity layers have dimensions on the scale of several hundred micrometers or less (thus the term “micro” in “microcavities”). In some applications, the microcavity layers are less than about one micrometer across, and as such are sometimes referred to as nanocavities.
One type of microcavity that is used in many applications is the photonic crystal cavity. Photonic crystal cavities are particularly suited for controlling and confining light in scales on the order of a cubic wavelength of light in the material. Photonic crystal cavities employ a photonic crystal membrane material having a multitude of holes and exhibiting a photonic band gap, often referred to as a forbidden zone in which light of a particular wavelength range is blocked. Light entering the photonic crystal cavity refracts through and partially reflects at interfaces between the photonic crystal structure and air at each of the holes. Light is selectively passed through the crystal structure in accordance with the size and arrangement of holes (or lack of holes in certain locations), the light's wavelength, the light's direction of travel, and the refractive index of the crystal structure and surrounding material.
In this regard, by controlling the type of crystal structure and holes therein, photonic crystals can be used to affect the motion of light. When used with light emitters, photonic crystals facilitate desirable control over the radiative properties of the emitters. High quality factor (Q) cavities defined in photonic crystals confine photons to a small volume, thus increasing the light-matter interaction, which can be useful in fields including quantum electrodynamics, optical detection, and light sources.
One microcavity application that has been the subject of increasing interest in recent times involves solid-state approaches to quantum information processing. Cavity quantum electrodynamics (CQED) is used to manipulate quantum bits (qubits) and, in some applications, involves the use of quantum dots coupled to optical cavities to facilitate qubit manipulation. Photonic crystal cavities are particularly attractive for such applications due to their small mode volume and high quality factor, and their amenability in integration of on-chip networks for information processing.
While photonic crystals have been useful in facilitating quantum information processing, many challenges have remained. For instance, spatially and spectrally matching emitters to photonic crystal cavities has been inconsistent and difficult. In applications involving quantum dots such as InGaAs quantum dots, spectral alignment has been particularly difficult.
These and other characteristics have presented challenges to the implementation of microcavity arrangements such as photonic crystal cavity arrangements and others, for applications such as quantum information processing.